1. Technical Field
The present disclosure relates to an apparatus and method for treating a structural collapse of thc human vertebrae, and more particularly, to an intervertebral device for treating collapsed vertebrae due to osteoporotic weakening.
2. Background of Related Art
Osteopenia is a bone condition resulting in a reduction in the normal content of the mineral calcium within a bone. The lack of calcium and associated collagen matrix, which binds the calcium into the bone structure, results in a weakening of the overall bone strength Osteoporosis, the pathological weakening of bone by severe demineralization, is brought about by advanced osteopenia and gives rise to significantly higher incidences of bone fractures. Osteopenia or osteoporosis in the spine can result in fracture collapse of one or more vertebrae or bone segments thereby shortening and deforming the spine. In some cases, these deformities inhibit a person's ability to function normally and may also affect a person's ability to breathe normally due to the collapse of the vertebral segments. These fractures or deformities are found most commonly among post-menopausal women, since it is known that the body's circulating level of the female hormone estrogen has a direct effect on osteopenia. Thus, when a woman's ovaries are either removed or stop manufacturing the estrogen hormone, osteoporosis is more likely to occur which could result in multiple bone fractures throughout the body.
Osteoporotic fractures are a common health problem and generally occur principally at the wrists, hip joints, ribs and collar bones. However, collapses involving the vertebrae, while the most common, are the least understood of the various fractures. Upon collapse of a spinal vertebra, the collapsing vertebra is transformed into the shape of a wedge having the narrow portion directed towards an anterior direction (front), thus causing the spine to exhibit the classic forward bending and the formation of a posterior hump. The collapse is usually opposite and away from the posterior compartment or spinal canal housing the spinal cord. A lesser occurring collapse of the posterior compartment of a spinal vertebra may result in a patient suffering from myelopathy due to cord compression. This total collapse of the vertebra with nearly complete loss of the vertebral body mass in all dimensions is quite rare except in some cases of metastatic cancer where the collapse may compress the spinal cord resulting in paraplegia or death.
Once the osteoporotic bone of the spine has become soft enough to permit a collapse under a relatively normal load, other bones or additional levels of the spine often fracture as well. This cascade of fractures creates a deformed, shortened spinal column. Secondary problems may then arise, such as interference with normal breathing, gait disturbance and a social stigma against the person's appearance. Collapse of a vertebral body occurs when there is a sudden increase in loading beyond that which the bone can tolerate, sometimes as the result of a normal event like sneezing or picking up a light object. The membrane surrounding the vertebral bone, the periosteum, is richly innervated with pain fibers which when disturbed by vertebral collapse administer pain signals, as well as, incite the formation of new bone growth. The vertebral collapse causes a loss of the contained vertebral bone marrow and an associated loss of vertebral body height. Due to a difference in construction and metabolism, the outer hard cortical enclosure of the vertebral bone does not suffer as much loss of mineral or strength as the softer interior cancerous bone.
The most important risk factors for bone fractures are an individual's: (1) age, (2) genetic factors, (3) environmental factors, (4) hormone levels, (5) presence of chronic diseases, and (6) the physical or radiologic characteristics of the bone. Although the true incidence of vertebral fracture is unknown, the evidence is clear that it increases exponentially with age in much the same way as for hip fractures. Between the ages of 60 and 90 years the incidence of vertebral fracture rises approximately 20-fold in women compared to a 50-fold increase in the risk of hip fracture. The problem of vertebral collapse is not limited to women alone, studies have shown that vertebral osteoporosis is seen in over 20% of men and women and is correlated with low dietary calcium intake and low serum vitamin D levels. Additional significant risk factors included cigarette smoking, low physical activity and long-term immobilization. The lowest levels of bone density were seen in women who suffered vertebral collapse fractures, most commonly in those having early menopause. It has also been shown that when the deformity or collapse of the vertebral bone segment is 4 cm or greater in vertebral height the likelihood of back pain is 2.5 times greater than when the collapse is of a lesser height. This likelihood is independent of how many vertebral levels are involved in fractures or whether or not the deformity involves anterior wedging, end plate failure or vertebral body crush. It is clear that vertebral collapse fractures are a significant clinical and economic problem.
The best treatment for osteoporosis is prevention particularly since the loss of bone strength that accompanies bone loss is not known to be reversible. Identification of those at risk by measurement of risk factors may help target prevention efforts. Many of the factors that are known to increase fracture risk in susceptible patients can be treated. Appropriate care or correction of risk factors include cigarette smoking, low circulating estrogen (usually associated with menopause), low physical activity and long-term immobilization, low dietary calcium intake and low serum vitamin D levels. Other treatable risk factors include: peptic ulcer, tuberculosis and illnesses or conditions that may cause dizziness, weakness and falling. These factors are particularly important in the elderly. It is clear that appropriate diet, exercise and supportive treatments are helpful in nearly all cases. However, a very large number of cases are not preventable since they are strongly influenced by genetic, medical or environmental circumstances. In such cases, certain new drugs including oral alendronate, an aminobisphosphonate or bisphosphonated etidronate taken daily, can progressively increase the bone mass (strength) in the body, including the spine and hip areas. Such treatments can reduce the incidence of vertebral fractures, the progression of vertebral fracture deformities and height loss in postmenopausal osteoporotic women. Unfortunately, these drugs have no beneficial effect to reverse the collapse after it has occurred. In fact, regardless of the predisposing factors, once the collapse has occurred, pain control and immobilization are essentially the only current treatments available. There exists no present method that can acutely reverse the collapse, lead to reconstitution of the vertebra and relieve the severe associated pain. The current mode of treatments include bed rest, the wearing of a rigid brace, sedatives, muscle relaxers, physical therapy modalities and other palliative measures. These treatments exhibit some value in pain reduction but generally the fractured or collapsed vertebra must be stabilized or fused for the severe pain to effectively subside.
More recently, spinal supporting injections of fast setting substances into the collapsed vertebrae have been used to fixate the vertebral collapse in order to stop the pain and suffering. Such injection substances include tricalcium phosphate, calcium carbonate, calcium hydroxyapatite, all of which act essentially like plaster of Paris. These injection materials will stop the progression of the vertebral collapse and subsequently be slowly converted into bone and thereby restore the strength of the collapsed segment. Also used as injection materials are polymerics, such as, fast setting polymethylmethacrylate mixed with powdered barium making the injected materials visible on X-ray images. However, none of these fast-setting materials and associated methods of use restore vertebrae height. In order to re-inflate or re-form the collapsed vertebra and restore the vertical height, the materials would have to be injected within the vertebrae under considerable pressure (up to 8 or 10 atmospheres, 116 to 145 psi 510 to 638 Newtons) so as to overcome the collapsing force, muscle pull and tissue recoil subjected upon the vertebra. At such high injection pressure, the injected material may leak through the fractured or collapsed portions of the vertebra and enter the adjacent major vessels, possibly causing an immediate and potentially lethal blockage. Further, these materials and other self-curing thermoplastics are highly viscous and cannot be injected through a reasonably sized hypodermic tube, cannula, catheter or introducer. The use of these materials also generate significant heat which may damage the sensitive bone cells leading to bone atrophy and delayed integration. In addition, the above-mentioned polymerics do not form or integrate into new bone and as such may create a new problem where the bone and the plastic material have a zone of non-union or pseudoarthrosis.
The embodiments of the present disclosure are described here to overcome the above limitations and achieve the goals of re-inflating or re-forming partially collapsed vertebrae, to restore the vertebral height, stabilize the fracture, integrate the injected material into bone and alleviate the severe pain associated with osteoporotic collapse. In addition, the techniques described herein may also be used in certain cases of complete or partial vertebral body collapse from erosion of the bone by a metastatic cancer or the like.